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What software is available out there to calculate the equilibrium in a set of reactions in aqueous solution? In particular, I'm interested in software general enough to simulate things like titration curves involving acido-basicity, complex formation, precipitation…

A web search turns up plenty of academic papers giving algorithms to find the equilibrium of such systems, but I'd like to find software that actually performs it. In particular, it would be really helpful if there existed such software that included a decent database of reaction constants for some well-known reactions (pKa for common acide-base couples, complexation and precipitation constants, etc.).

Edit: Apparently I was unclear: I'm not looking for molecular simulation codes, but for software that can calculate chemical equilibrium in solution from initial concentrations and a database of equilibrium constants for each possible reaction. The kind of thing teachers can use to predict titration curve and demonstrate the effect of various initial concentrations to students.

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ChemEQL is pretty nice in some instances and free, but it looks like it has been mostly abandoned.

I'm aware of Titrator, but it only runs on Windows and I've never had a chance to run it. It's also free.

I've heard good things about Visual MINTEQ, but it is Windows only and I've never had a chance to run it. Supposedly well maintained.

There is also PHREEQC, which sort of works on stuff other than Windows. I hear it is harder to use, but probably worth it.

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I've not tried it out, but implementations of ReaxFF may be suitable for your purposes. It performs atomistic finite-temperature simulation of reaction mixtures using a forcefield and as such is more general than your request but it seems like it could do the job.

It's available in ADF as an addon (note the nice demonstration of the time evolution of a combustion process), in LAMMPS (again, a cool demonstration of the concentration of species changing over time as a shockwave propagates through a crystal) and probably a lot of other packages.

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  • $\begingroup$ Sorry if I was unclear, I'm not looking for molecular simulation codes… See my edit to the question. $\endgroup$
    – F'x
    Commented Apr 26, 2012 at 3:06
  • $\begingroup$ @F'x - Ah, so ReaxFF is probably not so great as a didactic tool. You might want to look at Yenka chemistry, which might fit the bill either now or in the future. $\endgroup$
    – Richard Terrett
    Commented Apr 26, 2012 at 3:15
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After some more search, I have found two pieces of software who do titration simulation, but are (as far as I can tell) only available in French:

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While it is primarily constructed to perform titration and equilibrium calculations on metal coordination complexes, once you get used to its syntax HySS can be effectively used to simulate acid/base equilibria and titrations. One bonus of HySS is that it also treats solids (precipitates), which can be useful for, e.g., poorly soluble phenol derivatives.

Windows-only, unfortunately.

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